Gas turbine engines typically include a compressor, a fuel system, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high pressure air to the combustor. The fuel system delivers fuel such as liquid hydrocarbon fuel to the combustor, where it is mixed with the high pressure air and is ignited. Products of a combustion reaction in the combustor are directed into the turbine where work is extracted to drive the compressor and, sometimes, an output shaft. More specifically, combustors in gas turbine engines provide an energy release that drives the turbine. This energy release takes the form of high temperature gases. The handling of these gases drives the overall performance of the engine.
Recent advancements in such a gas turbine engine may use the liquid hydrocarbon fuel to cool hotter portions of the engine. In the process of cooling, the fuel can be heated to temperatures above the thermal stability limit of fuel, thereby resulting in the formation of coking including gum, tar, and varnish deposits within the fuel system. An approach for preventing such deposits involves removing or reducing the dissolved oxygen normally found in untreated jet fuel as it flows into the engine. Insufficient oxygen removal may occur due to failure or miscalibration of the oxygen removal system. The safety and efficient operation of a robustly engineered “hot fuel” system requires a means to detect such failure by measuring either oxygen concentration directly or the formation of coke deposits caused by insufficient oxygen removal. Thus, detection of coking is crucial to the operation and maintenance of gas turbine engines operating with fuel temperatures above thermal stability limits.
Traditional systems for measuring the percentage of entrained oxygen in the liquid hydrocarbon fuels are unsuitable for aircraft applications due to their size and weight. Further, typical systems may require regular calibration and adjustment resulting in variable and unreliable data outputs. Moreover, traditional systems do not provide an indication of factors, other than oxygen, that influence fuel quality and contribute to the coking of engine surfaces
Thus, there is a need for a system, apparatus, and method to detect coking in fuel systems, e.g., that operate above the fuel thermal stability limit and rely on an oxygen removal device to reduce accumulation of unwanted deposits such as carbon. Accordingly, the detection of coking by this method may facilitate a change in engine operating conditions to slow the coke deposition rate, or the timely maintenance of the engine fuel system for removal of unwanted deposits, thereby increasing engine efficiency and reliability.
For the purposes of promoting an understanding of the principles of the embodiments, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the embodiments is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the embodiments as described herein are contemplated as would normally occur to one skilled in the art to which the embodiment relates.